Film-Tech Forum ARCHIVE: NEC 1200 lamp adjustment

This is topic NEC 1200 lamp adjustment in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Richard May (Member # 2627) on 01-30-2013, 10:51 AM:

After changing lamps on 5 projectors at one location, I noticed the following. I adjusted the X,Y,Z controls in Z,X,Y order as said in the manual to get the highest readout. I went back and forth a few times to maximize the reading. On every projector the light reading was about 4 to 5 FL higher on the left side of the screen. The top and bottom readings were fine. What gives?

Posted by Marco Giustini (Member # 4544) on 01-30-2013, 02:42 PM:

don't trust the reading. Unfortunately in my experience it is not reliable. It works perfectly on a Barco or on a Christie - verified with a meter - but it's not reliable on a NEC.
NEC itself suggest on their manuals to find the highest reading and then check with a meter.

I'd do it by eye: use the controls as you were doing with a 35mm, you'll see some shadows moving on the screen, optimize the position of the lamp so the shadows are not visible. You'll gain a lot of light.

Posted by Richard May (Member # 2627) on 01-30-2013, 02:45 PM:

That's what I figured. I did try it by eye quickly, but had trouble shifting the light toward the right side of the screen. I'll try it again.

Posted by Carsten Kurz (Member # 5396) on 01-30-2013, 04:27 PM:

Does anyone know how this metering is actually done across the different brands? Single-sensor, multiple-sensor? Where?

- Carsten

Posted by Steve Guttag (Member # 268) on 01-30-2013, 09:55 PM:

A uniformity imbalance can be indicative a of a gain screen but more likely, in this case, that the "cold mirror" is not adjusted optimally to center the light from the reflector onto the integrator.

Posted by Richard May (Member # 2627) on 01-30-2013, 10:33 PM:

No gain screen here. It's weird that all 7 screens have the same issue. The light meter is working properly. You can see it just by looking at the screen.

Posted by Monte L Fullmer (Member # 2797) on 01-31-2013, 02:21 AM:

Any silver Screens at your location ?

Posted by Richard May (Member # 2627) on 01-31-2013, 10:28 AM:

No silver screens. As I've found with most of the theaters I service that now have digital, the installers were in and out quickly. I've had to readjust things that the installers screwed up. They're the certified ones. What a joke.

Posted by Marco Giustini (Member # 4544) on 01-31-2013, 12:20 PM:

It's a single sensor after the integrator rod, behind the fold mirror - just after the integrator rod) for a barco.
Christie catch the stray light from the vane where the integrator rod is, by the fold mirror.
I'm not sure about NEC.

Posted by Carsten Kurz (Member # 5396) on 01-31-2013, 06:36 PM:

Wondering how a single sensor can meet the purpose? Not with a simple maximising approach at least.

- Carsten

Posted by Marco Giustini (Member # 4544) on 02-01-2013, 02:21 AM:

I was skeptical at first, then I did some measurements and Barco and Christie are spot on... Sure, they assume your cold mirror is properly aligned.

Particularly Christie approach is stunning: a little box with a light sensor inside that catches the STRAY light in the cavity!! And it works!

Posted by Steve Guttag (Member # 268) on 02-01-2013, 06:34 AM:

I can confirm that Barco and Christie's method works very well. NEC can actually mislead (brighter, more even light is attained by not using the built in sensor). Now some NEC's sensors are fine but you can't bank on it.